Lightweight Large Pershing 1A

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I use 6mm depron for the cr's and fins(laminating them if needed for the fins.
I use 2mm for the skin.

I've tried 1mm but it is stiff and will kink in a curve, 3mm doesn't bend so well as 2mm.

I get mine from rcfoam.com In boxes of 10 or 20 it is around $8 or $9 a sheet. for 6mm and about $5 or $6 for 2mm.

But I have a local hobby shop that carries it as well for a dollar or two more a sheet.

It's not dirt cheap, but the cost of the rocket is not primarily the foam, it's tubes and other stuff. On this model I used 3 sheets of 6mm and 1.5 sheets of 2mm.

You could certainly use the paper covered foamboard from dollar tree for the cr's andstringers and use depron for the skin/fins, A lot of people soak and remove the cardboard from the foamboard to save weight.

Frank
 
Thanks so much. It is a lot more expensive than the foamboard and cardstock that I used. Buy my rocket turned out to be single use due the flooding. I think the depron also looks better is worth the investment. I might consider the hybrid approach that you suggested.
 
Wow, that looks fantastic Frank! I'm awestruck!

I was surprised I haven't seen foam rockets before (I was actually going to make some conversions of foam darts and rocket toys), but this is taking it to a whole new level. You should consider making a line of these...could open up a whole new market for rockets. I'd buy them. :)
 
Had a perfect maiden flight today on an H-180 at the tri cities rocketeers field! Perfectly straight, no coning, ejection right at the top, didn't even really arc over, no damage on recover, flight to 680 feet. I'm uploading a video in a bit. I also had another great flight on my Titan-DynaSoar in 11mph winds, handled it beautifully, a perfect flight on my Hellfire with an H-180 to 660' and a nice flight of my Jupiter C on an H-128..it was foam fest today!

Frank

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[video=youtube;jdqCXr7o6RE]https://www.youtube.com/watch?v=jdqCXr7o6RE"]https://www.youtube.com/watch?v=jdqCXr7o6RE[/video]

Here is the video
 
[video=youtube;jdqCXr7o6RE]https://www.youtube.com/watch?v=jdqCXr7o6RE"]https://www.youtube.com/watch?v=jdqCXr7o6RE[/video]

Here is the video
Nice flight! How much did the rocket weight without the motor?
 
Glad you could join us today Frank, your flights were just perfect. My favorites were the X-15, and Pershing flights, but they were all superb.
 
Thanks, that was a great launch.

The rocket weighs 65 oz without motor, but ready to fly, the airframe less recovery and altimeter is about 56 ounces.
 
Have you thought about kiting this like your gliders?
 
I've thought about it, but I don't know if there would be enough interest to make it worthwhile. The sheeting for the skin is large, box for all the components would not be small, etc...

Frank
 
Here are a few liftoff photo captures...One thing I did try, I have been running a plugged forward closure, but on the 29mm it still requires the delay element to be in place to provide sufficient tension for the o-rings to seat. Instead today, I filled the reservoir on the plugged closure with jb weld as per aerotech had instructed could be done, and then I did not need to use any of the forward delay parts. It made cleanup a breeze and reloading faster. Since these rockets don't go that high I don't need the tracking smoke. Effectively it makes it similar to the end burn closure they make for the 38mm. Worked fine on the H-180, H97 and H128. There didn't seem to be any errosion of the jb weld, even though they are core burners.

Frank

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Had my second flight in Washington this weekend. I unfortunately had a rare chute tangle. It actually tail slid slightly without arcing over and ejected cleanly but think the chute/nomex blanket hung up in the nose cone coupler section for a while, then the nomex blanket seemed to keep air from inflating the chute, and as it fell it spun the chute making the shroud lines twist and preventing any inflation as well. It's interesting the rocket fell completely flat, with the chute/nose cone dangling below the body. The altimeter decent rate showed only 24 fps as it fell. One good thing about being so light.

When it landed it broke in two, right where the joint in the foam structure goes from tapered nose to straight body. It turns out I built it in two halves and then slipped them over the stuffer tube. I was relying on the stuffer tube as the spine, so I didn't glue the two major foam pieces together with much glue. It turned out I also had a coupler joint in my 29mm stuffer tube at that same joint location. The stuffer tube coupler broke cleanly separating the two pieces with little damage to the foam portion. I was able to scrape/peel out the old coupler, make a new one that was much thicker and then re-attach the two pieces with little visible sign. Took two hours but she's back to flying condition. One fin did have some foam damage, but the carbon spar kept it from snapping and I was able to repair it.

Interestingly I flew H-180's in my 7" Jupiter C which weighs 4 pounds to 635 feet, the 8" pershing which weighs 4.5 pounds to 675 feet, and the 5# 7" hellfire to 730 feet, so even at this scale the extra mass does help altitude, with light weight and large diameter it really bleeds off speed quickly during coast. I would have though with these fat designs that drag would dominate the coast phase, and at some point more weight yields less altitude, but apparently these are still light enough that mass helps altitude slightly. Not that I care, they all look like they go to about the same altitude and fly really well. It's funny, they almost always go straight up, hang there and then eject during a backslide, they don't have enough mass/momentum to arc over for the most part....

I did have good luck with my launch pad. I had mounted the rail on a heavy door hinge, and installed a turnbuckle mechanism with a pull pin to attach the rail to one of the legs and allow me to quick relase the rail for loading, and adjust angle. Worked great. The locating pin I put in the bottom centering ring of my rockets which keys into the standoff plate on the rail also worked to hold the model in place and keep wind from blowing it back and forth on the rail.


Frank
 
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Here's another H-180 flight from today, great flying conditions.

Frank

[video=youtube;AYOvf2c9zwY]https://www.youtube.com/watch?v=AYOvf2c9zwY"]https://www.youtube.com/watch?v=AYOvf2c9zwY[/video]
 
Here is a great boost from this weekend at tri-cities Washington, on an I-200W, unfortunately the chute had a minor tangle and the rocket is so light it didn't get enough speed to pop it open, minor damage to one fin, so you could call this tumble recovery...I'd been using a slightly different folding method that was supposed to be better but I've had this one tangle and two others where they popped open only after some airspeed was gained in free-fall, so I went back to how I was doing it before and had three in a row that were successful. I'd use a chute bag, but again I don't know how much speed I get when it is falling to ensure a drogue would pull a bag off.
[video=youtube;lmIglwFZ8RI]https://www.youtube.com/watch?v=lmIglwFZ8RI&feature=youtu.be[/video]
 
Your foam rockets are inspirational - I really like big rockets on small motors! We have been working on a large upscale (4.9x, 12.75"x122") of the Binder Design Dragonfly. We are trying to keep it as light as possible with carbon fiber and balsa construction, but the darned thing is still going to weigh forty pound without the motor...

Are you planning to attend NXRS this year? I would love to check out some of your rockets in person if you do. We had a small pick-up launch in Silverton yesterday and your name came up (of course!) when we started talking big, lightweight rockets. As far as kitting them, I would buy a kit in a heartbeat - no shipping necessary, I'll pick it up!
 
How was the Silverton site? What's it like?

I'll probably be at nxrs but wont bring the foamies, sage would do too much damage.

Frank
 
How was the Silverton site? What's it like?

I'll probably be at nxrs but wont bring the foamies, sage would do too much damage.

Frank

I think it is a great spot, but I'm a little bit partial - it is across the road from my house... It is a good-sized field, about 1,000 acres in all. There is lots of grass, oats, and nursery stock with some Christmas trees and small patches of timber. It would be a great spot for foam rockets - unless they found a fence it is a pretty soft landing. I believe they are going to move forward and try to get a 5,000' waiver, possibly for a June launch if all goes well. We'll see!

I can imagine that Brothers' sage and rocks might be bad for a foam rocket.
 
That would be great if they can get a waiver, my stuff stays around 1k feet but is slightly over far101 weight.

Frank
 
I would think that kits would be to labor intensive to be practical. Selling detailed plan paks might practical however.
 
After many flights the foam pershing has taken some dents/dings. The rocket has had two tangled chutes early on that resulted in horizontal recovery that cracked a couple of the fins and broke a coupler joint in the stuffer tube that I had to fix. The carbon reinforced foam fins were patched, but after flying my Titan II and Atlas with the polycarbonate fins, I decided they are more robust although heavier. There was just always little chips/cracks I had to patch on the foam fins. Nothing major, just cosmetic, but annoying.

I also found that the bare depron gets dirty pretty easily and gets road rash more quickly, if I cover the foam with vinyl or trim monokote it makes it a lot more robust. So, this morning I pulled off the lower skin and pulled the fins out. I plan on making some 1/16" polycarbonate fins and some ply inserts with hardwood slots that the fins can sit into, that way the ply/hardwood take any landing bending load and it won't be transferred to the foam structure/skin. This will add around 8-10 ounces, but I know the structure/design can handle at least another pound and still fly well if needed. In the sims, the fin thickness has a drastic impact on the altitude, so even at an extra 10 ounces the rocket goes 200' higher with the thinner fins.
I've fixed the tangled chute issue by using a rocketman chute bag and chute.

I'll install the ply guide plates first, then skin the structure, apply the vinyl, then slot and install the fins last. I'll cover the fins with trim vinyl as well.

I'll post pictures if I remember to take them as I'm rebuilding.

I've also settled on the I-200 or I-205 single use as the ideal motors for all of the big foam rockets, 29mm keeps them light, I-200/205 gets them to around 1100' which is plenty high to see the whole flight.

Frank
 
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I cut out the first upper and lower fins and made my ply support guide plates and test fit them, looks like they will do fine. The polycarbonate is easy to work with, just score the cut lines three or four times with a box cutter then support and crack them at the cut line. Then just clean up the edges, cut the lightening holes with a hole saw.

I reinforced the upper joint between the straight and tapered body, and re-covered the lower third of the tapered area and then covered it in vinyl trim to match the upper portion, it feels nice and solid now. I need to fix a few little joints and cracked places from removing the old fins and then finish making up the ply plates and fins. Tomorrow I'll work on that and then have the fun of installing them. After the ply plates are installed so that the fins are aligned, I'll remove the fins, and put in some foam supports to help support the skin from coming up when I cut the fin slots after skinning.

Then I'll skin it, and cover with white and black trim vinyl. Then install the fins permanently. The lower fins seems fairly stiff, the upper fins seem like they have a bit of flex, not sure if I'll see any flutter or not, will have to decide if I want those in 3/32" or not.

Frank

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Got all the fins and plates cut, and cleaned up any little broken pieces in the internal structure this morning. I think I will go with 3/32" for the upper fins, they are right near the CG and will add maybe 2 oz more which should not shift the CG any.

Frank
 
Finished the mounting plates with their support rails, and installed them all using jb quick, my wife/daughter helped me hold them with the fins in place using a piece of angle aluminum to get them aligned with each other and along the long axis. They are pretty straight with each other and the long axis but the lower fins have about an eighth of an inch offset rotationally at the tip, I assume I have some slight twist of the lower and upper centering rings that isn't obvious by looking at them. I don't think this will make any difference in flight. I probably had this on the original foam fins but since they were much thicker I couldn't tell.

I cut the plates slightly undersized so I had a bit of movement allowed before the glue set to get them aligned, then pulled the fins out of the slots and added some foam pieces on each side of the fin slot which will allow a place for the skin to glue to and prevent buckling/popping out of the skin when I cut the fin slots. Tomorrow will re-skin the lower half and then cut the fin slots, then cover with vinyl.

You can see in the pictures how the slots will take the bending loads landing and not transfer any bend to the skin.

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Looks great, Frank. You are really making me think about attempting a big lightweight design!


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Thanks Dan! I was able to skin the lower half again with the help of my wife, and find/re-cut the slots, altimeter hatch and rail button locations in the skin. It's hard to see the clear fins but they are slid in place. Then I wrapped the black and white vinyl onto the lower half, made the hatch door with magnets and hinged it with vinyl trim and installed the rail buttons. I weighted it and it is now 5 pounds 5 ounces less motor and right at 6 pounds with an I-205, it looks like I'll have about 10" of cp/cg margin at least so more than a caliber without adding any nose weight.
I have to remember what glue I used on the polycarbonate fins on the titan/Atlas and then glue them in place and then cover the fins with white vinyl.

Frank

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Added some of the strap details and conduits with silver vinyl trim instead of making them 3d pieces and used a silver sharpie to make the outline of the fin steering plates, from a little distance it gives the effect without having to make and cover little bits and pieces....

Frank

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